1. Field of the Invention
This invention relates to an apparatus for subjectively measuring the refractive power of an eye.
2. Description of the Prior Art
The method of measuring the refractive power of the eye is grouped into the subjective examination and objective examination. Generally, however, objective examination is carried out to obtain the aim of the refractive power of the eye and finally, the refractive power of the eye is determined by the subjective examination.
In the conventional subjective examination, the refractive power of the eye has usually been determined with visual acuity as the standard. That is, a visual acuity measurement has been carried out by the use of a visual acuity examination mark and the refractive power of the eye has been determined with the measured visual acuity as the standard. In some cases, it has been difficult to judge from which visual acuity the refractive power of the eye should be obtained. This is because it cannot always be said that the best visual acuity is the best refractive power. This is known as the problem of over-rectification. Also, the visual acuity measurement itself has been carried out by comparing objects before and after in terms of time, and therefore, it has been very difficult for the examinee to judge which of the objects before and after can be seen better, causing fatigue of the examinee.